JP2018169544A - Plasma light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma light source for stably supplying a plasma medium between a center electrode and an external electrode. SOLUTION: A plasma light source 1 is connected to a coaxial electrode 10 in which a plurality of external electrodes 12 are arranged around a center electrode 11, and each of the center electrode 11 and the plurality of external electrodes 12, and the center electrode 11 and a plurality of the center electrodes 11. A voltage application unit 20 for applying a voltage between each of the external electrodes 12, a plasma medium material 41 for emitting the plasma medium 43, and a number of laser beams corresponding to a plurality of external electrodes 12 for the plasma medium material 41. A laser irradiation unit 30 is provided which irradiates 32 to emit the plasma medium 43 from the plasma medium material 41 and individually supplies the plasma medium 43 to the space between the center electrode 11 and the plurality of external electrodes 12. [Selection diagram] Fig. 1

Description

  The present invention relates to a plasma light source that generates extreme ultraviolet light.

  Conventionally, as a plasma light source for generating extreme ultraviolet light (EUV), for example, as described in JP-A-2013-89634, a plurality of external electrodes are arranged around a center electrode, It is known that a plasma is generated by applying a voltage between the center electrode and the external electrode while discharging the plasma medium while discharging the plasma medium, and generating extreme ultraviolet light by the transition radiation of the plasma. .

JP 2013-89634 A

  In this kind of plasma light source, it is desired to stably generate plasma and emit extreme ultraviolet light stably. That is, in order to emit extreme ultraviolet light with a sufficient amount of light, it is necessary to generate stable plasma between the center electrode and each external electrode. In the plasma light source described above, a plurality of external electrodes are arranged around the center electrode, and discharge is performed between the center electrode and each external electrode, thereby generating a planar plasma centering on the center electrode. . At this time, if there are variations in a plurality of discharges performed between the center electrode and each external electrode, it becomes difficult to generate desired plasma. For example, when there are strong and weak discharges for each external electrode, non-uniform plasma is generated around the center electrode, and desired extreme ultraviolet light cannot be emitted.

  Thus, in this technical field, development of a plasma light source that stably generates uniform plasma with little bias around the center electrode and stably emits extreme ultraviolet light is desired.

  That is, the plasma light source according to one embodiment of the present invention is connected to the coaxial electrode in which a plurality of external electrodes are arranged around the center electrode, and the center electrode and the plurality of external electrodes, respectively. A voltage applying unit for applying a voltage between each of the electrodes, a plasma medium material for releasing the plasma medium, and irradiating the plasma medium material with a number of lasers corresponding to a plurality of external electrodes from the plasma medium material A laser irradiation unit that discharges the plasma medium and supplies the plasma medium to a space between the center electrode and each of the plurality of external electrodes.

  According to this plasma light source, the plasma medium material is irradiated with a number of lasers corresponding to the plurality of external electrodes to discharge the plasma medium, and the plasma medium is supplied to the space between the center electrode and the plurality of external electrodes. To do. This makes it possible to individually adjust the amount of plasma medium supplied to the plurality of spaces between the center electrode and each external electrode and the supply timing. For this reason, the bias of the plasma generated between each external electrode and the center electrode can be reduced, and the plasma generated around the center electrode can be equalized. Thereby, the extreme ultraviolet light radiated | emitted from plasma can be generated stably.

  Further, in this plasma light source, a plurality of plasma medium materials may be arranged corresponding to the number of arrangements of the plurality of external electrodes, and the laser irradiation unit may emit the plasma medium by irradiating each of the plasma medium materials with a laser. . In this case, by arranging one plasma medium material for one external electrode, it becomes easier to supply the plasma medium individually for each space between the center electrode and the external electrode, and the plasma medium material is generated around the center electrode. Plasma equalization can be improved.

  In the plasma light source described above, a partition wall that partitions the space between the adjacent center electrode and the external electrode may be provided. In this case, diffusion of the emitted plasma medium is suppressed, and a desired amount of the plasma medium can be accurately supplied to the space between the center electrode and each external electrode. Therefore, the bias of the plasma generated in each space between each external electrode and the center electrode can be reduced, and the equalization of the plasma generated around the center electrode can be improved.

  In the plasma light source described above, a protrusion extending in the axial direction may be formed on at least one of the opposing positions of the center electrode and the external electrode. In this case, the discharge position between the center electrode and the external electrode is stabilized by forming at least the protrusions of the center electrode and the external electrode. Therefore, a desired plasma can be generated stably.

  Furthermore, the above-described plasma light source may be configured with two coaxial electrodes facing each other. In this case, desired plasma can be stably generated in each of the two coaxial electrodes, and stable emission of extreme ultraviolet light is possible.

  According to the present invention, it is possible to stably generate plasma and stabilize emission of extreme ultraviolet light.

FIG. 1 is a diagram showing a configuration of a plasma light source according to the first embodiment of the present invention. FIG. 2 is a perspective view of the center electrode and the external electrode in the plasma light source of FIG. FIG. 3 is a diagram showing laser irradiation in the plasma light source of FIG. FIG. 4 is a diagram showing a current path formed during operation of the plasma light source of FIG. FIG. 5 is a diagram for explaining the operation of the plasma light source of FIG. FIG. 6 is a view showing partition walls in the plasma light source according to the second embodiment. FIG. 7 is a view showing partition walls in the plasma light source according to the second embodiment. FIG. 8 is a diagram illustrating a modification of the plasma light source according to the embodiment.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.
(First embodiment)

  As shown in FIG. 1, the plasma light source 1 according to the first embodiment is configured by arranging two coaxial electrodes 10 to face each other, and is a so-called opposed plasma focus type plasma light source. When this opposed plasma focus type plasma light source 1 operates, first, a voltage is applied between the center electrode 11 and the external electrode 12. Then, by inputting some sort of trigger, a ring-shaped initial plasma is generated between the center electrode 11 and the external electrode 12. The initial plasma moves toward the tip of the center electrode 11 by electromagnetic force. The initial plasma converges in the radial direction at the tip of the center electrode 11 and reaches a high temperature and high density state. Then, by causing the plasmas that have reached the tips of the respective center electrodes 11 to collide with each other, plasma with higher temperature and higher density is formed. Extreme ultraviolet light is generated from this high temperature and high density plasma.

  One method for generating initial plasma is a method in which a plasma medium is evaporated (ablated) with laser light. By irradiating a solid or liquid plasma medium material with laser light, the plasma medium is emitted to generate medium vapor. A discharge is generated between the center electrode 11 and the external electrode 12 through the medium vapor. The plasma medium material may be solid, liquid, or gas, and is selected according to the wavelength of light to be generated.

  The plasma light source 1 according to the present embodiment is applied to, for example, an exposure apparatus for manufacturing a semiconductor element. The plasma light source 1 is configured to generate extreme ultraviolet light (EUV) having a wavelength of 13.5 nm, for example. The plasma light source 1 enables photolithography to form a fine pattern by generating extreme ultraviolet light.

  The plasma light source 1 includes a pair of coaxial electrodes 10 that generate plasma, a voltage application unit 20 that applies a voltage to the coaxial electrodes 10, a laser irradiation unit 30 that performs laser irradiation, and a plasma medium material 41 that discharges a plasma medium. I have.

  The pair of coaxial electrodes 10 and 10 are accommodated in the chamber 2, are arranged so as to face each other on the axis A, and are provided so as to abut each other on the tip side. The pair of coaxial electrodes 10 are arranged symmetrically with respect to the virtual central plane P. A constant space (space) is provided between the pair of coaxial electrodes 10. One or a plurality of exhaust pipes 3 are provided in the chamber 2, and a vacuum pump (not shown) is connected to the exhaust pipe 3. The inside of the chamber 2 is maintained at a predetermined degree of vacuum. The chamber 2 is grounded.

  The coaxial electrode 10 is configured by arranging a plurality of external electrodes 12 around a center electrode 11. The coaxial electrode 10 is an electrode unit that discharges in a space between the center electrode 11 and each external electrode 12, and the center electrode 11 and the external electrode 12 are made of a conductor. The base end sides of the center electrode 11 and the plurality of external electrodes 12 are supported by the insulator 13. The center electrode 11 is a rod-like body and extends along the axis A. The external electrode 12 is also a rod-like body and is provided in the same direction as the center electrode 11.

  In the pair of coaxial electrodes 10, 10, the center electrode 11 of the left coaxial electrode 10 extends toward the right coaxial electrode 10. The center electrode 11 is preferably made of a metal that is not easily damaged by high temperatures. The center electrode 11 is made of a refractory metal such as tungsten (W) or molybdenum (Mo). The axis A of the center electrode 11 is orthogonal to the above-described center plane P.

  The external electrode 12 of the left coaxial electrode 10 is a rod-shaped body extending toward the right coaxial electrode 10. The external electrode 12 may extend in a direction inclined with respect to the axis A. For example, the external electrode 12 may extend in a direction parallel to the side surface so that the distance from the side surface of the center electrode 11 to the external electrode 12 is always constant. The external electrode 12 is preferably made of a metal that is not easily damaged by high temperatures. The external electrode 12 is made of a refractory metal such as tungsten (W) or molybdenum (Mo).

  FIG. 2 is a perspective view of the center electrode 11 and the external electrode 12. In FIG. 2, for convenience of explanation, the illustration of the plasma medium material 41 is omitted.

  As shown in FIG. 2, the external electrode 12 is disposed around the center electrode 11. The external electrode 12 has a predetermined interval with respect to the center electrode 11. The plurality of external electrodes 12 are arranged at equal intervals or substantially equal intervals in the circumferential direction of the center electrode 11. FIG. 2 shows the case where four external electrodes 12 are arranged around the center electrode 11, but the number of external electrodes 12 is not limited to four. May be. Further, it can be set as appropriate according to the size and shape of the center electrode 11 and the external electrode 12, the distance between them, and the like. By disposing a plurality of external electrodes 12 around the center electrode 11, initial discharge (for example, creeping discharge) is generated between the center electrode 11 and the external electrode 12. This initial discharge forms a planar plasma.

  Protrusions 11c and 12c extending in the axial direction are formed at opposite positions of the center electrode 11 and the external electrode 12. For example, the center electrode 11 is configured as a prism or pyramid having a quadrangular cross section, and the four corners function as the protrusions 11c. The external electrode 12 is formed, for example, as a prism or pyramid having a triangular cross section, and a corner facing the center electrode 11 functions as a protrusion 12c. Here, the opposed positions of the center electrode 11 and the external electrode 12 include positions that are substantially opposed to each other, and the protrusions 11c and 12c may function as ends that generate discharge. The axial direction of the center electrode 11 and the external electrode 12 means the longitudinal direction of the center electrode 11 and the external electrode 12 when the center electrode 11 and the external electrode 12 are formed as rods.

  As described above, the protrusions 11c and 12c are formed at the opposite positions of the center electrode 11 and the external electrode 12, so that when the discharge occurs between the center electrode 11 and the external electrode 12, the protruding protrusions 11c and 12c Discharging is performed between them, and the discharge position in the circumferential direction of the center electrode 11 is stabilized. As a result, plasma generation can be stabilized through stable discharge.

  Only one of the protrusion 11c of the center electrode 11 and the protrusion 12c of the external electrode 12 may be formed. For example, a cylindrical body may be used as the external electrode 12 and the formation of the protrusion 12c may be omitted. In some cases, a cylindrical body or a conical body is used as the center electrode 11, and the formation of the protrusion 11c is omitted. Even in these cases, the discharge position can be stabilized by forming the one protrusion 11c or the protrusion 12c. Further, the center electrode 11 may have a polygonal cross section other than a square cross section, depending on the number of external electrodes 12 installed. The external electrode 12 may have a polygonal cross section other than a triangular cross section. By using members having a polygonal cross section as the center electrode 11 and the external electrode 12, the corners can function as the protrusions 11c and 12c even though they are simple shapes, and the durability of the protrusions 11c and 12c is improved. Can be planned. Moreover, since it is a simple shape, manufacture of the center electrode 11 and the external electrode 12 becomes easy.

  In addition, when the circular shape cross-sectional object is used as the center electrode 11 and the external electrode 12, the protrusion 11c and the protrusion 12c may protrude from the surfaces of the center electrode 11 and the external electrode 12 and extend in the axial direction.

  In FIG. 1, the insulator 13 is, for example, a disk-shaped ceramic plate. The insulator 13 supports the base portions of the center electrode 11 and the external electrode 12 and defines the distance therebetween. The insulator 13 electrically insulates the center electrode 11 and the external electrode 12 by supporting the center electrode 11 and the external electrode 12 apart from each other.

  The voltage application unit 20 applies a discharge voltage to the coaxial electrode 10. The voltage application unit 20 includes, for example, two high-voltage power supplies (HV Charging Devices) 21 and 22. The output side of the first high-voltage power supply 21 is connected to the center electrode 11 of one coaxial electrode 10 (for example, on the left side in the drawing). The common side of the first high-voltage power supply 21 is connected to the external electrode 12 corresponding to the center electrode 11. The first high-voltage power source 21 applies a positive discharge voltage higher than that of the external electrode 12 corresponding to the center electrode 11. The first high voltage power supply 21 may apply a negative discharge voltage lower than that of the external electrode 12 corresponding to the center electrode 11. The output side of the second high-voltage power source 22 is connected to the center electrode 11 of the other coaxial electrode 10 (for example, on the right side in the drawing). The common side of the second high-voltage power supply 22 is connected to the external electrode 12 corresponding to the center electrode 11. The second high-voltage power supply 22 applies a positive discharge voltage higher than that of the external electrode 12 corresponding to the center electrode 11. The second high voltage power supply 22 may apply a negative discharge voltage lower than that of the external electrode 12 corresponding to the center electrode 11. The common side of any high-voltage power supply may be grounded. In the following description, the first high-voltage power supply 21 is simply referred to as the power supply 21. Similarly, the second high-voltage power supply 22 is simply referred to as the power supply 22.

  A line inductively coupled using a Rogowski coil or the like may be provided on the common side of the power supplies 21 and 22. With these lines, the current passing through the center electrode 11 (that is, all discharge currents) can be observed with an oscilloscope (Oscilloscope).

  The plasma light source 1 further includes an energy storage circuit 26 that stores the discharge voltage from the voltage application unit 20 as discharge energy for each external electrode 12. The energy storage circuit 26 includes a plurality of capacitors C that individually connect the center electrode 11 and each external electrode 12. By providing the capacitor C for storing discharge energy for each external electrode 12, discharge can occur in all the external electrodes 12. That is, even when a slight shift occurs in the discharge generation timing, a large amount of discharge energy is prevented from being consumed by the first discharge generated. By providing the energy storage circuit 26, an ideal multiple discharge having symmetry is obtained around the center electrode 11 in the coaxial electrode 10.

  The plasma light source 1 further includes a discharge current blocking circuit 28 that blocks the discharge current from returning to the voltage application unit 20. The discharge current blocking circuit 28 includes an inductor L that connects between the external electrode 12 and the voltage application unit 20 (specifically, the common side of the power supplies 21 and 22). Since the inductor L has a sufficiently high impedance with respect to the discharge current, the discharge current that has passed through the center electrode 11 and the external electrode 12 can be returned to the energy storage circuit 26 that is the generation source thereof. Thereby, it is possible to prevent the discharge energy accumulated in the capacitor C from being supplied to the external electrodes 12 other than the external electrode 12 directly connected to the capacitor C. As a result, it is possible to prevent the generation distribution of discharge in the circumferential direction of the center electrode 11 from being biased.

  The operation of the voltage application unit 20 described above will be described. First, charges are stored (charged) in the capacitor C in advance by the power supplies 21 and 22. Then, when a plasma medium is supplied between the center electrode 11 and the external electrode 12, a current flows from the positive electrode side to the negative electrode side of the capacitor C. As this current, a current corresponding to the amount of charge accumulated in the capacitor C flows in a pulsed manner according to the time constant of the electric circuit. That is, the charge flows in the order of the center electrode 11, the multiple discharge 6, and the external electrode 12, and finally returns to the negative electrode side of the capacitor C. While this current is flowing, the planar plasma formed by the multiple discharge 6 moves to the tip of the center electrode 11 and converges as a single plasma at the tip to emit light.

  The laser irradiation unit 30 includes a laser device 31, a beam splitter (half mirror) 34, and a mirror 35. Laser light 32 emitted from the laser device 31 is irradiated onto the plasma medium material 41 via the beam splitter 34 and the mirror 35. This laser light irradiation causes ablation, and plasma medium vapor (medium vapor) is generated. The laser device 31 is, for example, a YAG laser, and outputs a fundamental wave or a double wave of the fundamental wave as a short pulse laser beam for ablation.

  The laser device 31 emits laser light 32. The laser beam 32 is branched into at least two laser beams 32 a and 32 b by an optical element such as a beam splitter 34 and a mirror 35, and irradiated to the plasma medium material 41. On the surface of the plasma medium material 41 irradiated with the laser beams 32a and 32b, a part of the plasma medium material 41 is emitted as a plasma medium by ablation. Here, the plasma medium is particles or medium vapor of the plasma medium material 41, and the plasma medium contains neutral gas or ions.

  In addition, when the laser beams 32 a and 32 b are irradiated, the discharge voltage from the voltage application unit 20 has already been applied to the center electrode 11 and the external electrode 12 of the coaxial electrode 10. Therefore, when the ablation described above occurs, a discharge is induced between the center electrode 11 and the external electrode 12. Further, a planar plasma is formed by this discharge. There is a possibility that the location where discharge occurs is limited to the irradiation region of the laser beam 32 and the vicinity thereof. Accordingly, it is preferable to irradiate a plurality of laser beams 32 at intervals along the circumferential direction of the axis A.

  FIG. 3 is a schematic view of the center electrode 11, the external electrode 12, and the plasma medium material 41 as viewed from the center plane P side, and shows laser irradiation to the plasma medium material 41.

  The plasma medium material 41 is disposed in the vicinity of the center electrode 11 and the external electrode 12. For example, a plurality of plasma medium materials 41 are arranged corresponding to the number of external electrodes 12 arranged. In FIG. 3, four plasma medium members 41 are arranged for the four external electrodes 12. Specifically, the plasma medium material 41 is disposed at a position between the adjacent external electrodes 12, 12. The plasma medium material 41 is installed with the irradiation surface of the laser light 32 a (32 b) facing the space between the center electrode 11 and the external electrode 12. Thereby, the plasma medium 43 emitted in the normal direction from the irradiation surface by laser irradiation can be supplied to the space between the center electrode 11 and the external electrode 12.

  As the plasma medium material 41, for example, a substance corresponding to the wavelength of light to be emitted is used. When extreme ultraviolet light (EUV) having a wavelength of 13.5 nm is generated, for example, lithium (Li) is used as the plasma medium material 41. As the plasma medium material 41, xenon (Xe), tin (Sn), or the like may be used. When extreme ultraviolet light of 6.7 nm is required, at least one of gadolinium (Gd), terbium (Tb), or the like is used as the plasma medium material 41. The plasma medium material 41 is, for example, a solid material, and is disposed at a predetermined position by being supported by the insulator 13. The plasma medium material 41 may be supported on the insulator 13 via a support member (not shown) extending from the insulator 13 in the axial direction of the center electrode 11. When a liquid material is used as the plasma medium material 41, a tube body that opens toward the space between the center electrode 11 and the external electrode 12 may be used, and the plasma medium material 41 may be supplied through the tube body.

  As shown in FIG. 3, the plasma medium material 41 is irradiated with a number of laser beams 32 a corresponding to the plurality of external electrodes 12. Here, the four external electrodes 12 are irradiated with four laser beams 32a. That is, the plasma medium material 41 is arranged for each external electrode 12, and one laser beam 32 a is irradiated to one plasma medium material 41. The plasma medium 43 is emitted from the plasma medium material 41 by the irradiation of the laser beam 32a, and the plasma medium 43 is individually supplied to the space between the center electrode 11 and the plurality of external electrodes 12. By performing laser irradiation in this way, it is possible to individually adjust the amount of plasma medium supplied to the space between the center electrode 11 and the external electrode 12 and the supply timing. In FIG. 3, in the four spaces between the center electrode 11 and each external electrode 12, the amount of plasma medium and the supply timing can be individually adjusted. For this reason, the bias of the plasma generated between the center electrode 11 and each external electrode 12 can be reduced, and the equalization of the plasma generated around the center electrode 11 can be improved. Therefore, it is possible to stably generate extreme ultraviolet light emitted from the plasma.

  In order to adjust the amount of the plasma medium supplied to the space between the center electrode 11 and the external electrode 12, the light amount or the energy amount of the laser beam 32a applied to the plasma medium material 41 may be increased or decreased. For example, an attenuator can be arranged in the middle of the optical path of the laser beam 32a to adjust the light amount of the laser beam 32a. Further, the amount of energy of the laser beam 32a irradiated on the plasma medium material 41 can be adjusted by changing the position of the lens that focuses the laser beam 32a on the plasma medium material 41 and adjusting the focal position. By increasing the light amount or the energy amount of the laser beam 32a irradiated to the plasma medium material 41, the amount of the plasma medium supplied to the space between the center electrode 11 and the external electrode 12 can be increased. On the other hand, the amount of the plasma medium supplied to the space between the center electrode 11 and the external electrode 12 can be reduced by reducing the light amount or the energy amount of the laser beam 32a irradiated to the plasma medium material 41. . Thus, the amount of plasma medium supplied to the space between the center electrode 11 and the external electrode 12 can be individually adjusted. For this reason, the bias of the plasma generated between the center electrode 11 and each external electrode 12 can be reduced, and the plasma generated around the center electrode 11 can be equalized.

  In order to adjust the supply timing of the plasma medium supplied to the space between the center electrode 11 and the external electrode 12, the irradiation timing of the laser beam 32a applied to the plasma medium material 41 may be changed. For example, when the laser beam 32a is irradiated with a pulse, the irradiation timing of the laser beam 32a can be changed by changing the optical path length of the laser beam 32a. By increasing the optical path length of the laser beam 32a, the irradiation timing of the laser beam 32a can be delayed. On the other hand, the irradiation timing of the laser beam 32a can be advanced by shortening the optical path length of the laser beam 32a. As described above, the supply timing of the plasma medium supplied to the space between the center electrode 11 and the external electrode 12 can be individually adjusted. For this reason, the bias of the plasma generated between the center electrode 11 and each external electrode 12 can be reduced, and the plasma generated around the center electrode 11 can be equalized.

  Here, the electrical state in the plasma light source 1 in operation will be described. FIG. 4 shows a current path K formed by the coaxial electrode 10 and the voltage application unit 20 when the polarity of the center electrode 11 is positive. As shown in FIG. 4, the current path K reaches the center electrode 11 from the positive electrode side of the capacitor C through an electric circuit. Here, although the center electrode 11 and the external electrode 12 are physically separated from each other, during operation, a plasma medium exists between the center electrode 11 and the external electrode 12, so that multiple discharges 6 are generated. . Therefore, the current reaches from the center electrode 11 to the external electrode 12 through the plasma medium. Then, the external electrode 12 reaches the negative electrode side of the capacitor C through an electric circuit.

  The plasma medium material 41 is not incorporated in the current path K formed by the voltage application unit 20 and the coaxial electrode 10. In addition, the current flowing through the coaxial electrode 10 when plasma is generated does not flow through the plasma medium material 41. That is, the plasma medium material 41 is electrically insulated from the current path K.

  The plasma medium material 41 only needs to be electrically disconnected from the current path K. The plasma medium material 41 electrically disconnected from the current path K may be electrically grounded. According to this electrical configuration, charging of the plasma medium 43 is prevented. Further, according to this electrical configuration, the potential of the plasma medium 43 can be made constant without being affected by the high voltage of the center electrode 11 and the external electrode 12.

  Further, the plasma medium material 41 electrically disconnected from the current path K may be connected to a predetermined potential. Specifically, the holding material for holding the plasma medium material 41 is formed of a conductive material such as metal, and a potential is applied to the holding material. For example, according to the configuration connected to a relatively low potential, the potential of the plasma medium material 41 can be positively stabilized. Further, ionization of the plasma medium 43 is promoted. The ionized plasma medium 43 is more likely to trigger a discharge than the neutral gas. As an example, when the plasma medium material 41 is lithium and a positive potential is applied to the plasma medium material 41, a part of lithium floats as lithium ions (positive ions) by laser ablation. Positive ions that reach the discharge space are more likely to be a discharge trigger than neutral gas.

  In addition, as long as the plasma medium material 41 is electrically disconnected from the current path K, the plasma medium material 41 may be in an electrically floating state.

  Next, the operation of the plasma light source 1 will be described with reference to FIG.

  5A shows the state when the laser beams 32a and 32b are irradiated, FIG. 5B shows the state when the multiple discharge 6 is generated, and FIG. 5C shows the state where the multiple discharge 6 is moving. FIG. 5D shows the state when the tip of the multiple discharge 6 reaches the electrode tip, FIG. 5E shows the state when the high-temperature and high-density plasma 7 is generated, and FIG. (F) part has shown the state of the high-density plasma 7 made high temperature.

  First, the inside of the chamber 2 is maintained at a temperature and pressure suitable for generating the plasma 7. A discharge voltage is applied to the coaxial electrode 10 before discharge by the voltage application unit 20. As shown in part (a) of FIG. 5, the laser light 32 a and 32 b are irradiated on the plasma medium material 41 in a state where a discharge voltage is applied. Immediately thereafter, discharge occurs between the center electrode 11 and the external electrode 12. A discharge occurs between each of the plurality of external electrodes 12 and the center electrode 11. As shown in part (b) of FIG. 5, multiple discharges 6 distributed in the circumferential direction of the center electrode 11 are obtained.

  At this time, as shown in FIG. 3, the plasma medium material 41 is arranged according to the number of external electrodes 12 installed, that is, the number of spaces between the central electrode 11 and the external electrode 12. Laser light 32a (32b) is irradiated according to the number of spaces between them. Specifically, four spaces between the center electrode 11 and the external electrode 12 are respectively irradiated with laser light 32a, and the plasma medium 43 is supplied to the spaces. Thereby, the amount of plasma medium supplied to the plurality of spaces between the center electrode 11 and each external electrode 12 and the supply timing are individually adjusted, so that multiple discharges generated around the center electrode 11 can be prevented in the circumferential direction. Can be equalized.

  Then, as shown in part (c) of FIG. 5, the multiple discharge 6 moves in a direction (direction toward the center plane P) discharged from the electrode by the self magnetic field. The shape of the multiple discharge 6 at this time is substantially radial when viewed from the axis A.

  At this time, as shown in FIG. 3, since the protrusion 11c is formed on the center electrode 11 and the protrusion 12c is formed on the external electrode 12, a discharge is performed between the protrusion 11c and the protrusion 12c, The multiple discharge 6 moves along the protrusions 11c and 12c. Therefore, the multiple discharge 6 is performed stably.

  Here, since the plasma light source 1 includes the energy storage circuit 26, the probability of occurrence of the multiple discharge 6 is increased by the cooperation of the energy storage circuit 26 and the plurality of external electrodes 12. From the viewpoint of facilitating the formation of the multiple discharge 6 as compared with the case where a continuous tubular (tubular) external electrode is employed, the plurality of external electrodes 12 arranged discontinuously at intervals. It is advantageous.

  Thereafter, as shown in FIG. 5D, the multiple discharge 6 reaches the tip of the coaxial electrode 10. When the multiple discharge 6 reaches the tip of the center electrode 11, the starting point of the discharge current shifts from the side surface 11b of the center electrode 11 to the end surface 11a. By this current transition, the plasma containing lithium (Li) that has moved with the pair of multiple discharges 6 is converged, and becomes high density and high temperature.

  Since this phenomenon proceeds at the coaxial electrode 10 with the center plane P interposed therebetween, the initial plasma is pushed out from one coaxial electrode 10 toward the other coaxial electrode 10. As a result, the initial plasma receives pressure from both directions along the axis A and moves to an intermediate position where the coaxial electrode 10 faces (that is, the position of the central plane P), and a single plasma 7 having a plasma medium as a component. Is formed.

  Then, as shown in FIG. 5E, even after the plasma 7 is formed, current continues to flow through the multiple discharge 6 so as to surround the plasma 7 as a whole. Keep near.

  While the multiple discharge 6 is occurring, the plasma 7 is increased in density and temperature, and ionization of ions including lithium (Li) proceeds. As a result, as shown in part (f) of FIG. 5, plasma light 9 including extreme ultraviolet light is emitted from the plasma 7. In this state, when the current continues to flow through the multiple discharge 6, the plasma light 9 can be generated for a long time.

  The plasma light source 1 is supplied with a plasma medium 43 between the center electrode 11 and the external electrode 12 during operation. The plasma medium 43 induces a discharge between the center electrode 11 and the external electrode 12. When the multiple discharge 6 is generated between the center electrode 11 and the external electrode 12, a current path K is formed through the center electrode 11, the plasma medium 43, and the external electrode 12. Here, since the plasma medium material 41 is electrically insulated from the current path K, the current flowing through the current path K does not pass through the plasma medium material 41. When current flows through the conductor, Joule heat is generated, but since no current flows through the plasma medium material 41, Joule heat is not generated. Therefore, the temperature rise of the plasma medium material 41 is suppressed and the state of the plasma medium material 41 is stabilized, so that the ablation of the plasma medium material 41 can be stably generated. Therefore, the vapor of the plasma medium 43 can be stably supplied between the center electrode 11 and the external electrode 12.

  As described above, according to the plasma light source 1 according to the present embodiment, the plasma medium material 41 is irradiated with the number of laser beams 32 (32a, 32b) corresponding to the plurality of external electrodes 12 to emit the plasma medium 43. Thus, the plasma medium 43 is supplied to the space between the center electrode 11 and each of the plurality of external electrodes 12. This makes it possible to individually adjust the amount and supply timing of the plasma medium 43 supplied to the plurality of spaces between the center electrode 11 and each external electrode 12. For this reason, the bias of the plasma generated between each external electrode 12 and the center electrode 11 can be reduced, and the plasma generated around the center electrode 11 can be equalized. Thereby, the extreme ultraviolet light radiated | emitted from plasma can be generated stably.

  Further, according to the plasma light source 1 according to the present embodiment, a plurality of plasma medium materials 41 are arranged corresponding to the number of arrangement of the plurality of external electrodes 12, and the laser irradiation unit 30 applies laser light to each of the plasma medium materials 41. 32 is irradiated to release the plasma medium 43. Thereby, it becomes easy to supply the plasma medium 43 individually for each space between the center electrode 11 and the external electrode 12, and the equalization of plasma generated around the center electrode 11 can be improved.

  Further, according to the plasma light source 1 according to the present embodiment, the protruding portion 11c or the protruding portion 12c extending in the axial direction is formed in at least one of the opposed positions of the center electrode 11 and the external electrode 12. Thereby, the discharge position between the center electrode 11 and the external electrode 12 is stabilized. Therefore, a desired plasma can be generated stably.

Furthermore, according to the plasma light source 1 according to the present embodiment, the two coaxial electrodes 10 and 10 are opposed to each other. For this reason, desired plasma can be stably generated in each of the two coaxial electrodes 10 and 10. Further, the plasma generation timing of each coaxial electrode 10 can be adjusted. Therefore, stable emission of extreme ultraviolet light is possible.
(Second embodiment)

  Next, the plasma light source 1a according to the second embodiment will be described.

  The plasma light source 1a according to the present embodiment is configured in substantially the same manner as the plasma light source 1 according to the first embodiment described above, and includes a partition wall 14 that partitions an adjacent space between the center electrode 11 and the external electrode 12. Thus, the plasma light source 1 is not provided with the partition wall 14.

  6 and 7 are views showing partition walls in the plasma light source according to the present embodiment. As shown in FIG. 6, a partition wall 14 is provided so as to partition the adjacent space between the center electrode 11 and the external electrode 12. In FIG. 6, since four external electrodes 12 are arranged around the center electrode 11, four spaces are formed between the center electrode 11 and each external electrode 12. For this reason, one partition 14 is provided between adjacent spaces. For example, the partition wall 14 is supported by an insulator 13 (see FIG. 1) that supports the center electrode 11 and the external electrode 12 on the base end side. As the partition wall 14, for example, a plate formed of an insulating material may be used.

  The partition wall 14 is a wall body that suppresses the diffusion of the plasma medium 43 supplied to the space between the center electrode 11 and the external electrode 12 into the adjacent space. The partition wall 14 may not completely partition the adjacent space between the center electrode 11 and the external electrode 12. In other words, a sufficient effect can be expected even with a structure that can reduce the movement of the plasma medium 43 to the adjacent space.

  As shown in FIG. 7, the partition wall 14 is provided so as to cover a region where the plasma medium material 41 is arranged with respect to the axial direction of the center electrode 11 and the external electrode 12 (A direction in FIG. 7). That's fine. For example, the partition wall 14 is provided so as to extend from the insulator 13 to the distal end side of the center electrode 11 and the external electrode 12 to the installation position of the plasma medium material 41. In FIG. 7, for convenience of explanation, only the partition walls 14 corresponding to the pair of center electrode 11 and external electrode 12 are shown.

  According to the plasma light source 1a according to the present embodiment, in addition to the operational effects of the plasma light source 1 according to the first embodiment described above, the partition wall 14 that partitions the space between the adjacent center electrode 11 and the external electrode 12 is provided. By being provided, diffusion of the emitted plasma medium 43 is suppressed, and a desired amount of plasma medium can be accurately supplied to the space between the center electrode 11 and each external electrode 12. Therefore, the bias of the plasma generated in each space between each external electrode 12 and the center electrode 11 can be reduced, and the equalization of the plasma generated around the center electrode can be improved.

  The present invention has been described in detail above based on the above-described embodiment. However, the present invention is not limited to the above embodiments. The present invention can be variously modified without departing from the scope of the claims.

  For example, in each of the above-described embodiments, the plasma medium material 41 is disposed away from the center electrode 11, but the plasma medium material 41 may be disposed attached to the center electrode 11. Specifically, as shown in FIG. 8, a plasma medium material 41 is attached to the outer periphery of the center electrode 11, and a plurality of laser beams 32 corresponding to the number of external electrodes 12 arranged with respect to the plasma medium material 41 are supplied to the plasma medium material 41. May be irradiated. In FIG. 8, four laser beams 32 are applied to the four external electrodes 12. Even in this case, it is possible to individually adjust the amount and supply timing of the plasma medium 43 supplied to a plurality of spaces between the center electrode 11 and each external electrode 12. For this reason, the bias of the plasma generated between each external electrode 12 and the center electrode 11 can be reduced, and the plasma generated around the center electrode 11 can be equalized. Thereby, the extreme ultraviolet light radiated | emitted from plasma can be generated stably. In the plasma light source of FIG. 8, the partition wall 14 may be provided. In this case, diffusion of the emitted plasma medium 43 is suppressed, and a desired amount of plasma medium can be accurately supplied to the space between the center electrode 11 and each external electrode 12. Therefore, the bias of the plasma generated in each space between each external electrode 12 and the center electrode 11 can be reduced, and the equalization of the plasma generated around the center electrode can be improved.

  Further, in each of the above-described embodiments, the case where the present invention is applied to the plasma light source of the opposed plasma focus system in which the two coaxial electrodes 10 and 10 are arranged to face each other has been described. It can also be applied to plasma light sources other than the system. That is, the present invention may be applied to a plasma light source that discharges and emits ultraviolet light with one coaxial electrode 10.

DESCRIPTION OF SYMBOLS 1, 1a Plasma light source 2 Chamber 3 Exhaust pipe 6 Multiple discharge 7 Plasma 9 Plasma light 10 Coaxial electrode 11 Center electrode 11a End surface 11b Side surface 12 External electrode 13 Insulator 14 Partition 20 Voltage application part 21 Power supply 22 Power supply 26 Energy storage circuit 28 Discharge current blocking circuit 30 Laser irradiation unit 31 Laser device 32 Laser beam 34 Beam splitter 35 Mirror 41 Plasma medium material 43 Plasma medium A Axis C Capacitor P Center plane L Inductor K Current path

Claims (5)

A coaxial electrode in which a plurality of external electrodes are arranged around the central electrode;
A voltage application unit that is connected to each of the center electrode and the plurality of external electrodes and applies a voltage between the center electrode and each of the plurality of external electrodes;
A plasma medium material for discharging the plasma medium;
The plasma medium material is irradiated with a number of lasers corresponding to the plurality of external electrodes to discharge the plasma medium from the plasma medium material, and the space is formed between the center electrode and the plurality of external electrodes. A laser irradiation unit for supplying a plasma medium;
A plasma light source comprising: A plurality of the plasma medium materials are arranged corresponding to the number of arrangement of the plurality of external electrodes,
The laser irradiation unit irradiates each of the plasma medium materials with the laser to release the plasma medium.
The plasma light source according to claim 1.   The plasma light source according to claim 1 or 2, wherein a partition wall that partitions a space between the adjacent center electrode and the external electrode is provided.   The plasma light source according to any one of claims 1 to 3, wherein a protrusion extending in the axial direction is formed on at least one of the opposed positions of the center electrode and the external electrode.   The plasma light source according to any one of claims 1 to 4, wherein the two coaxial electrodes are opposed to each other.

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